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¹ Division of Fish Health Management, Central Institute of Freshwater Aquaculture, Kausalyaganga, Bhubaneswar-751002, Odisha, India DOI : 10.4194/1303-2712-v16_4_07 Viewed : 4715 - Downloaded : 4504 In order to study the diversity of putative lactic acid bacteria (LAB) in freshwater fish, 76 strains of LAB were isolated from intestines and identified by phenotypic tests and 16S rDNA gene sequencing. Phenotypic characterization of the isolates allowed the identification of 18 clusters at 78% similarity level by Hierarchical cluster analysis. Functional evenness index (E value) a measure of phenotypic diversity, was found to be quite high (0.7 approximately) in most of the samples. 16S rDNA gene sequencing identified the isolates as different strains of Lactobacillus plantarum, Lactobacillus pentosus, Lactobacillus fermentum, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus brevis, Lactobacillus reuteri, Lactobacillus salivarius, Pediococcus pentosaceus, Pediococcus acidilactici, Weissella paramesenteroides, Weissella cibaria, Enterococcus faecium and Enterococcus durans. Lactobacillus plantarum was found to be the dominating strain and LAB occurred more frequently in hindgut. Most of the strains showed good survival in acid and bile tolerance tests and antimicrobial activity against fish pathogen Aeromonas hydrophila. Different bacteriocin producing genes were detected in several strains by PCR. Selective strains with probiotic attributes could be potential candidates for freshwater aquaculture practices. Keywords : Lactic acid bacteria, freshwater fish, phenotypic diversity, 16S rDNA gene, probiotic